1. Field of the Invention
The present invention relates generally to the field of marine propulsion systems, and particularly to systems designed for pleasure craft, such as fishing boats, and the like. More particularly, the invention relates to a propulsion system employing dual electric motor propulsion units near a stern region of a watercraft, with a forward rudder for additional control.
2. Description of the Related Art
Various systems and configurations have been proposed and are currently in use for navigating watercraft. Depending upon the size and use of the watercraft, these systems include both internal combustion-driven propulsion units, and electric motor drives. In the former case, outboard motors may be mounted to a transom of a boat, and used alone or in tandem to produce the desired thrust for navigating the boat for its intended use. Similarly, inboard motors typically include an internal combustion engine housed within a compartment of the hull, with a driven propeller extending through the hull to propel the boat in a similar manner.
Electric motor drives for watercraft have been developed, and are particularly well suited to slow-speed and special purpose applications. For example, trolling motors and electric outboards are available for slow-speed navigation, and are well suited to fishing boats, wherein quiet operation is essential. Indeed, electric motor drives are the favored solution for such activities, and are typically used in tandem with outboard or inboard motor systems to provide flexibility and to enhance the utility of the craft for a wide range of activities.
While propulsion systems of the type described above are generally suitable for many uses, they are not without drawbacks. For example, internal combustion engine-driven systems are simply unsuitable for applications in which low noise levels, low emission levels, and low speed navigation are important. Similarly, conventional electric propulsion systems often do not provide a desired degree of navigational flexibility, and suffer from a tendency to become entangled in weeds or other plants growth, to contact submerged objects and obstructions, and so forth. Moreover, conventional trolling motor systems typically require that a drive unit and directional unit be rigidly mounted to a deck surface, both during deployment and when stowed. Consequently, a section of the deck becomes essentially unusable and is severely obstructed. These systems also detract from the aesthetic appeal of the watercraft, and may provide an unacceptable level of aerodynamic drag, both when deployed and when stowed.
There is a need, therefore, for an improved propulsion and navigation system for watercraft, particularly for pleasure craft. There is, at present, a particular need for a system which would eliminate or reduce the need for deck encumbrances, while providing effective low-speed navigation and steering. Furthermore, there is a need for a system which can be retrofitted to existing boat designs, as well as incorporated into new designs, controlled through relatively intuitive control devices, and provide as user-friendly a navigation system as possible.
The present invention provides a technique for propelling and navigating a watercraft designed to respond to these needs. The technique is useful on existing boat designs, but is particularly well suited to new designs wherein propulsion units and a navigational rudder may be directly incorporated into the watercraft, and received within recesses provided in a boat hull. In accordance with certain aspects of the technique, a dual electric motor stern drive is provided in which propulsion units are mounted aft of a transverse centerline of a watercraft hull. In one embodiment, the drives arc mounted in a stern region below the boat transom. Each drive includes an electric motor which drives a prop. The electric motor is conveniently mounted within a cavity of the hull, reducing the need to seal and protect the electric motor from the surrounding water. A torque transmitting assembly extends through the hull to a prop of each unit. The prop is driven by the electric motor to produce thrust, either in forward or reverse directions. Thrust from the drives is combined to produce a desired resultant thrust for propelling the watercraft in a variety of directions.
The technique further provides a rudder which is preferably positioned forward of the transverse centerline. The rudder affords enhanced controllability of the navigation system, and substantially reduces the leeway made by the craft as a result of wind currents and the like. Moreover, the rudder may be provided in a permanently extended position, or may be retractable within a cavity provided in the hull. Furthermore, the rudder may be stationary (i.e., angularly fixed with respect to the hull) or may be directional. In the latter case, the directional or angular orientation of the rudder may be adjusted in cooperation with the thrust produced by the propulsion units to navigate the boat effectively, even in the presence of wind and water currents. The propulsion units and the rudder may be networked so as to offer enhanced controllability, such as via a single operator command device.